I personally kept my Canon lenses and went for the adaptor for my a7s. In fact I kept my 5dmark III and use it exclusively for closeup mug shots, surprisingly the softness of the footage is very flattering for this kind of shots, I find the a7s or even my C100 too sharp for this.
C100 and a7s owner here. As much as I love my a7s, the C100 is a proper and complete video camera that is easier to use than any DSLR form factor type camera. Although I can take my a7s in darker places, the C100 has very nice colors and very nice skin tones that only require a few tweaks in post unlike the a7s which take more work. I require very fast turn around so every little savings in time helps. Oh another interesting function the C100 is tis dual pixel. I prefer focusing manually but I was surprised how useful was the dual pixel AF was especially in many run and gun situations.